Vehicle seat occupancy detection systems are nowadays widely used in vehicles, in particular in passenger cars, for providing a seat occupancy signal for various appliances, for instance for the purpose of a seat belt reminder (SBR) system or an activation control for an auxiliary restraint system (ARS). Seat occupancy detection systems include seat occupancy sensors that are known to exist in a number of variants, in particular based on capacitive sensing. An output signal of the seat occupancy detection system is usually transferred to an electronic control unit of the vehicle to serve, for instance, as a basis for a decision to deploy an air bag system to the vehicle seat.
It is further known in the art to use a portion of an electric seat heater of a vehicle seat as a sensor in a capacitive seat occupancy detection system. For example, patent application publication DE 41 10 702 A1 describes a vehicle seat with an electric seat heater comprising a conductor which can be heated by the passage of electrical current through it. The conductor is located in the seating surface and forms a part of a capacitive sensor for detecting a seat occupancy of the seat.
In vehicle seats that are equipped with one or more seat heater members, it is known to be beneficial to incorporate at least one seat heater member in a capacitive measurement of a vehicle seat occupancy detection system, due to an inherent strong capacitive coupling to a seat frame of the vehicle seat and the benefit of hardware savings.
In such vehicle seats there exists a risk of compromising the reliability of the seat occupancy detection system by a failure of the seat heater member that is involved in the capacitive measurement. Therefore, detection of a seat heater member failure is desirable.
It is therefore an object of the invention to provide a capacitive vehicle seat occupancy detection system with an improved capability of detecting failures of a seat heater member that is involved in the capacitive measurement of the vehicle seat occupancy detection system.